1. Field of the Invention
The present invention relates to a diaphragm for acoustic equipment, e.g. loudspeaker, headphone and microphone. More particularly, the present invention relates to a diaphragm which can have excellent acoustic characteristics as a diaphragm for acoustic equipment use on account of the fact that as compared with the conventional material for a diaphragm it is possessed of a high strength and a high elasticity, and moveover its weight is light and internal loss is moderate.
2. Prior Art
Generally speaking, as a diaphragm for acoustic equipment, it is desired that all of the following conditions are satisfied.
(1) The density is small. PA1 (2) The Young's modulus is large. PA1 (3) The velocity of propagation of long waves is large. PA1 (4) The internal loss of vibration is moderately large.
Besides the above, when considering the following formula: EQU V=(E/.rho.).sup.1/2
(wherein V=velocity of sound, E=Young's modulus, and .rho.=density), in order to increase the velocity of sound it is required that the density is small and the Young's modulus is large.
Heretofore, as the diaphragms having a large Young's modulus use had often been made of a light metal such as aluminum, titanium, magnesium, beryllium, boron, etc.
However, the acoustic diaphragms made of aluminum, titanium, magnesium, or the like, could not obtain a fully satisfactory specific Young's modulus E/.rho., and the acoustic diaphragms made of beryllium, boron and others, though they could obtain an extremely large specific Young's modulus, had problems such that they cost too much more than other materials because their raw materials are not only highly expensive but also considerably difficult to carry out their industrial processing.
In view of the above-described defects of the materials of the conventional diaphragms the object of this invention is to provide a diaphragm which can have excellent acoustic characteristics by making the most of the physical characteristics of carbon.
As well-known, carbon is possessed of the physical and chemical properties widely ranging from those of crystalline carbon such as diamond or graphite to those of amorphous carbon such as carbon black, charcoal, etc.
The present inventor who made an elaborate investigation in order to make a diaphragm exhibit the aimed manihold functional characteristics by combining these carbon materials in designing so as to fit the functions required, formerly invented a process for preparation of a wholly carbonaceous diaphragm which is obtained by orienting to a high degree the crystals of the highly crystalline graphite having a high elastic modulus in the direction of the surface of the film, using resin charcoal as a binder (Japaneses Patent Application Kokai No. 23,298/1986). The diaphragm prepared in accordance with the invention proved to be a diaphragm which had excellent physical characteristics exhibiting the characteristic properties possessed by graphite as the result of the high degree orientation of the highly crystalline graphite.
The present inventor further continued the elaborate investigation for improving a diaphragm for acoustic equipment use, and thus, by paying their attention to the fact that the honeycomb structure which is recently in wide use as the structural materials in the field of the space navigator has a high specific elastic modulus as well as a high internal loss owing to the unique structure, it was led to this invention.